This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. The goal of this project is to investigate the mechanisms by which glutamatergic retinal inputs form synaptic contacts on GABAergic and glutamatergic postsynaptic tectal neurons. Afferent projections form connections with both glutamatergic and GABAergic postsynaptic neurons. The connections from single afferents to different types of postsynaptic neurons have different properties, such as the strength of transmission or plasticity in response to trains of activity. These differences in cell-type specific synaptic properties have been shown to be critical for information processing. Furthermore, connections with excitatory and inhibitory neurons are differentially sensitive to changes in visual experience. Our work has shown that individual retinotectal axons form direct connections with both excitatory and inhibitory tectal neurons and that the strength of the connections differs according to the identity of the postsynaptic cell. We propose to test whether glutamatergic retinal ganglion cell connections with glutamatergic or GABAergic postsynaptic cells differ in their ultrastructural properties and response to changes in afferent activity patterns using serial block-face SEM (SBFSEM) reconstruction of retinal axons and their targets from intact Xenopus visual system.